Abstracts Chemistry

Synthesis of precursors of a highly pyramidalized alkene and ab initio calculations on methylenecyclopropane, cyclopropene, and 1,3-diradicals

by William T. G Johnson

The synthesis of precursors for the highly pyramidalized olefin 3,7-dimethyltricyclo[3.3.0.03,7]octane are described within. Three computational projects are also contained in this thesis. In the first, the increase in strain energy that results from placing a trigonal center in a cyclopropane ring is shown to be due to the loss of a stabilizing cyclopropyl C-H bond, not an increase in angle strain. In the second, the singlet state of a derivative of the trimethylene diradical is shown to be stabilized to such an extent relative to the closed cyclopropane as to make the two isomers nearly isoenergetic. The barrier for closure of the trimethylene derivative via enforced disrotation is also shown to be quite high, owing to the substitution at C-2 of the diradical with silyl groups. In the third, previous experimental results are reinterpreted showing that spiropentane opens via conrotation, in agreement with qualitative molecular orbital theory. A long range interaction between a terminal methyl group in pentane-2,4-diyl and the more distant radical center is described. The interaction is found to be stabilizing when C-3 is substituted with donors, and destabilizing when C-3 is substituted with acceptors.